test_denominator = ->
  run_test [

    "denominator(2/3)",
    "3",

    "denominator(x)",
    "1",

    "denominator(1/x)",
    "x",

    "denominator(a+b)",
    "1",

    "denominator(1/a+1/b)",
    "a*b",

    # denominator function expands

    "denominator(1/(x-1)/(x-2))",
    "x^2-3*x+2",
  ]